A variety of techniques have been employed to measure deposition of atmospheric contaminants (see for example: Methods of Air Sampling and Analysis, 3rd ed., J. P. Lodge, Jr. Ed., 1989, Lewis Publishers, Inc. Chelsea, Mich.). Known techniques include the use of devices which incorporate glycerol-coated plates or pans, Teflon sheets, containers of water, polyurethane foam plugs, carbon or other adsorbent traps and glass fiber or paper filters. Such devices suffer from the adverse consequences of instability, complexity, and mechanical operation. For example, samplers having open containers of liquids (so called impingers) suffer from evaporative losses, microbial contamination, and the effects of changing weather conditions.
Air filtration based samplers are subject to variable filtration rates as particulate matter is accumulated on the surface or deposited within the filter media. The particulate matter acts as an additional filtration media with the potential of reducing flow rates of air through the system. Also, the particulate matter often adsorbs vapor phase organic compounds at a rate significantly greater than the original inert filter thus, resulting in imprecise or inaccurate residue values.
Mechanical or active sampling devices require power to operate pumps, vortex tubes, precipitators, etc. In addition, in most instances such sampling devices must be calibrated for each set of analyses. All such configurations are subject to various failures.
Passive samplers based on air diffusion are often subject to errors caused by variations in air face velocity. Trapping media suitable for use in diffusion samplers are confined primarily to adsorptive solids. Because commonly used diffusion membranes are porous to water vapor, the solid adsorbents are susceptible to the deleterious effects of humidity.
Laboratories involved in the analysis of trace quantities of organic pollutants, such as polychlorinated biphenyls (PCBs), must have atmospheres which are practically free of these chemicals to prevent false-positive results, i.e., reporting that a chemical was present in a sample when it actually came from the laboratory environment.
To ensure that airborne contamination of samples is not a problem in laboratories, a simple and effective way to monitor air at very low levels for targeted analytes (organics) is needed. Unfortunately, current methods usually require complex sampling apparatus such as calibrated pumps and are usually not integrative over sufficient time intervals to pick up ultra-trace level contaminants and episodic releases.